This invention relates to pulsed beams of charged particles. In particular, it is directed to measurement and control of the phase of bunches of charged particles in a beam.
It is frequently important to have an accurate measurement of the phase of bunches of charged particles in a repetitive pulsed beam. It is also frequently of importance to control the bunching of such particles in response to the error from a fixed reference in order to maintain control of the phase. This is sometimes referred to as reducing pulse-separation jitter. It may also be desirable to control the signal input to a buncher to reduce the time spread in a bunch of charged partilces. In research accelerators precision control of bunching of a beam that is injected into an RF accelerator makes it possible to exercise more precise control on the output energy. Furthermore, the control of the phase is facilitated by the generation of an output signal marking the centroid of a pulse of charges and this information is useful as a time marker for time-of-flight experiments and the like. These considerations are not only of importance to the operation of a particle accelerator for research purposes but also have extensions to the use of precision particle beams in controlling diagnostic and therapeutic x-rays and timing pulses for injection in attempts to achieve thermonuclear fusion by beams of ions.
A pulsed beam is commonly achieved by generating a dc beam and passing that beam through a buncher. The buncher accelerates some charged particles and decelerates others so that after a period of drift at varying speeds a portion of the beam is compacted into a bunch. This is similar to the bunching performed in a klystron, for example. However, as with a klystron, variations in the accelerating voltage, the initial entering velocity of the charged particles or voltages from any other power supplies in the system can cause spread in the width of the pulse of charged particles that has been bunched. If the bunch is to be subjected to further acceleration, then the accelerated bunch will probably be spread still further in energy.
It is an object of the present invention to provide a method and means of measuring and controlling the phase of a bunch of charged particles in a particle accelerator.
Other objects will become apparent in the course of a detailed description of the invention.